import React, { Component } from 'react'

export default class Count extends Component {

    state = {
        count: 0
    }

    increment = () => {
        const {value} = this.selectNumber;
        const {count} = this.state;
        this.setState({
            count: count + value * 1
        })
    }

    decrement = () => {
        const {value} = this.selectNumber;
        const {count} = this.state;
        this.setState({
            count: count - value * 1
        })
    }

    incrementIfOdd = () => {
        const {value} = this.selectNumber;
        const {count} = this.state;
        if(count%2 !== 0) {
            this.setState({
                count: count + value * 1
            })
        }
    }

    incrementAsync = () => {
        const {value} = this.selectNumber;
        const {count} = this.state;
        setTimeout(() => {
            this.setState({
                count: count + value * 1
            })
        }, 3000);
    }

    render() {
        return (
            <div>
                <h1>当前求和为：{this.state.count}</h1>
                <select ref={c => this.selectNumber = c}>
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3">3</option>
                </select>&nbsp;
                <button onClick={this.increment}>+</button>&nbsp;
                <button onClick={this.decrement}>-</button>&nbsp;
                <button onClick={this.incrementIfOdd}>当前求和为奇数再加</button>&nbsp;
                <button onClick={this.incrementAsync}>异步加</button>
            </div>
        )
    }
}
